Wire coated with a fluorocarbon polymer cross-linked with esters of sulfonyl dibenzoic acid

ABSTRACT

Esters of sulfonyl dibenzoic acid of the formula ##SPC1## 
     In which R 1  and R 2  are selected from the group consisting of allyl and methallyl. The compounds are useful as additives to accelerate the crosslinking of polymeric materials.

This is a division of application Ser. No. 528,019 filed Nov. 29, 1974.

This invention relates to esters of sulfonyl dibenzoic acid and to their use as crosslinking agents for polymeric compositions.

I have discovered a new class of compounds, the diallyl, dimethallyl and mixed allyl methallyl esters of 4,4'-sulfonyl dibenzoic acid. Specifically, the new compounds have the structural formula ##SPC2##

In which R₁ and R₂ are independently selected from the group consisting of allyl and methallyl radicals. These compounds have been found to act as excellent plasticising and crosslinking agents for a variety of polymeric compounds. The new compounds are particularly useful as additives for accelerating the crosslinking of high temperature processing fluorocarbon polymers, that is polymers which are extruded, or in certain instances, molded at temperatures above 260° C. These include, for example, polymers and copolymers of ethylene-tetrafluoroethylene, ethylene-chlorotrifluoroethylene, vinylidene fluoride, tetrafluoroethylene-vinylidene fluoride, tetrafluoroethylenehexafluoropropylene, vinylidene floride-hexafluorpropylenetetrafluoroethylene and the like. The new compounds have been found to improve the elevated temperature mechanical properties of the crosslinked polymers. They also act as plasticizing agents for the polymers prior to crosslinking. Further, polymers containing the compounds have been successfully extruded onto wire.

The new compounds may be produced by reacting the sulfonyl dibenzoic acid with thionyl chloride to produce the corresponding diacyl chloride. The diacyl chloride is reacted with allyl alcohol, methallyl alcohol or a mixture of allyl and methallyl alcohol. The 4,4'-sulfonyl dibenzoic acid starting material is a known, commercially available compound, described for example in Beilstein: Handbuck des Organische Chemie, 10, pg. 186. Alternatively, these new compounds can be prepared by other methods including direct esterification, catalyzed esterification or interchange esterification from saturated esters of the sulfonyl dibenzoic acid. Additionally, the compounds can be produced from the sulfonyl dibenzoic acid dinitrile or dialdehyde or like intermediates by known techniques.

The diallyl or dimethallyl esters of the invention may be used alone, or in combination with other polyfunctional crosslinking additives. Among such additives useful in combination are the diallylic and dimethallylic esters of phenyl indan as shown in U.S. Pat. No. 3,763,222. A number of other polyfunctional crosslinking additives, useful in combination with the present esters, are disclosed in application Ser. No. 402,302 filed Oct. 1, 1973. Examples of the latter are diallyl brassylate, triallyl trimesate, triallyl trimellitate and triallyl isocyanurate. Others will occur to those skilled in the art.

The crosslinking compound or compounds are added in amounts sufficient to plasticize the polymer or polymer blends for processing and to impart deformation resistance upon cross-linking. This amount may range from 0.5 to 20 parts by weight per 100 parts by weight of polymer, but will normally be from 1 to 10 parts of the crosslinker per 100 parts of polymer. The polymer or polymers and crosslinking compounds are blended, processed in the melt at an elevated temperature for a period of time sufficient to melt process, but insufficient to crosslink. The formed mixture is then cooled to ambient temperature and irradiated at a dosage between, for example, about 5 and 20 megarads.

The following examples illustrate the practice of the invention. Unless otherwise indicated, all parts are by weight.

EXAMPLE 1

This example illustrates the preparation of diallyl 4,4'-sulfonyl dibenzoate. To a suitable reaction vessel equipped with a thermometer and reflux condenser was charged 200 grams (0.65 mole) of 4,4'-sulfonyl dibenzoic acid, 189 ml. (2.61 moles) of thionyl chloride and 5 ml. of dimethylformamide (DMF). The so charged mass was heated carefully until solution occurred and then refluxed overnight. Excess thionyl chloride was distilled, first at atmospheric pressure and finally at the aspirator. Then, 134 ml. (1.96 moles) of allyl alcohol were added during a period of 3 hours and the reaction mixture was heated under reflux for another 2 hours. Most of the excess allyl alcohol was stripped and the residual molten mass slurried twice with dilute sodium carbonate solution and finally with water. After collection and air drying on a Buchner funnel, the solid product was crystallized from ethanol acetone (80:20) to afford white crystalline material in 85% yield. The material was characterized by infrared spectroscopy as the diallyl ester of 4,4'-sulfonyl dibenzoic acid, M.P. 137° C (at a 5° C/minute differential scanning calorimeter rate).

EXAMPLE 2

This example illustrates the preparation of dimethallyl 4,4'-sulfonyl dibenzoate. Employing the procedure of Example 1, 100 grams (0.33 mole) of 4,4'-sulfonyl dibenzoic acid, 95 ml. (1.31 moles) of thionyl chloride and 3 ml of dimethyl formamide were refluxed with exclusion of moisture for eight hours. Excess thionyl chloride was removed at atmospheric pressure and finally under aspirator vacuum. Then, 110 ml (1.31 moles) of methallyl alcohol were added to the resulting diacyl chloride and after reflux for three hours, the mixture was poured into a dilute solution of sodium carbonate in water. Crystallization of the crude material from acetone furnished oyster-white product in 53% yield. The product was characterized by infrared spectroscopy as the dimethallyl ester of 4,4'-sulfonyl dibenzoic acid, M.P. 157° C (at a 5° C/minute differential scanning calorimeter rate).

The diallyl ester compounds possess solubility or plasticizing properties which render them compatible with a variety of polymeric systems. For example, certain of the fluorocarbon polymers are known to exhibit unusually high chemical resistance and tend to reject plasticizer or solvent which is incorporated therein. The compounds of the invention are compatible with these fluorinated polymers in spite of the known high resistance of these polymers to solvation and swelling. The diallyl esters, when incorporated in these polymers, permit extrusion at considerably lower temperature profiles.

Table I shows the decrease in torque values achieved by the incorporation of five parts of diallyl 4,4'-sulfonyl dibenzoate in 100 parts of various fluorocarbon polymers as compared with the same polymers without additive.

                  TABLE I                                                          ______________________________________                                                              Mixing       Torque                                                 Additive   Chamber      (Meter-                                      Polymer   (Parts)    Temp. (° C)                                                                          grams)                                       ______________________________________                                         E/TFE.sup.1                                                                              None       288           850                                         "          5         288           750                                         E/CTFE.sup.2                                                                             None       260          1750                                         "          5         260          1700                                         PVDF.sup.3                                                                               None       288          1075                                         "          5         288           900                                         ______________________________________                                          .sup.1 Ethylene-tetrafluoroethylene copolymer.                                 .sup.2 Ethylene-chlorotrifluoroethylene copolymer.                             .sup.3 Polyvinylidene fluoride homopolymer.                              

The torque data was obtained in "Brabender" Sigma type mixer using a 63 gram total charge, in each case employing the noted temperature at a shear rate of 80 r.p.m.

The reduction in torque values indicates that the polymeric compositions containing the diallyl ester can be processed at lower temperatures, for example, to provide continuous thin wall extrusions or at equivalent temperatures to provide thinner wall extrusions.

The following examples illustrate the excellent mechanical and aging properties of crosslinked polymeric compositions containing the compounds of the invention.

EXAMPLE 3

A polymeric composition was prepared by powder blending 200 grams of an ethylene-tetrafluoroethylene copolymer with 10 grams of diallyl 4,4'-sulfonyl dibenzoate, produced by the process of claim 1, and 1.0 grams of magnesium oxide. The blended mixture was compression molded at 254° C and subjected to irradiation at 10and 20 megarad doses in a 1.5 mev. electron beam accelerator to produce samples of crosslinked slabs of the polymeric composition. The samples had the following mechanical properties at room temperature (about 25° C) and at elevated temperatures.

                  TABLE II                                                         ______________________________________                                                          Mechanical Properties                                         ______________________________________                                         Radiation Dose (MR)                                                                               10         20                                               ______________________________________                                         At Room Temperature                                                            Tensile Strength (psi)                                                                            5989       4577                                             Elongation (at 10"/min.) (%)                                                                      200        96                                               At 250° C                                                               Tensile Strength (psi)                                                                            549         402                                             Elongation (at 10"/min.) (%)                                                                      333         135                                             Hot Modulus (%)*                                                               at 275° C/50 psi                                                                           42         37                                               Deformation (%)                                                                at 100° C/500 grams                                                                        No change after 1                                                              hour under specified                                                           load.                                                       ______________________________________                                          *Hot Modulus indicates the % extension of a sample strip of crosslinked        polymer after heating the sample above the melting temperature of the          uncrosslinked polymer, applying the indicated stress to the sample and         cooling to room temperature.                                             

EXAMPLE 4

The irradiation crosslinked samples of Example 3 were aged at 260° C. Samples were tested for tensile strength and elongation after cooling to room temperature. The excellent aging qualities of the crosslinked samples are shown in Table III.

                                      Table III                                    __________________________________________________________________________                         Aging Period (Days)                                        __________________________________________________________________________                  Radiation                                                         Test         Dose (MR)                                                                             0   1   3   5   7   11  15                                 __________________________________________________________________________     Tensile Strength (psi)                                                                      10     5989                                                                               4479                                                                               4588                                                                               4113                                                                               4345                                                                               4407                                                                               4296                               Elongation (%)                                                                              10      200                                                                               81  88  44  50  31  25                                 Tensile Strength (psi)                                                                      20     4577                                                                               4688                                                                               4441                                                                               4736                                                                               4341                                                                               4259                                                                               4122                               Elongation (%)                                                                              20     96   100                                                                               60  50  44  19  6                                  __________________________________________________________________________

EXAMPLE 5

Additional crosslinked compositions were prepared as set forth in Example 3 substituting however an ethylene-chlorotrifluoroethylene (E/CTFE) copolymer and a polyvinylidene fluoride (PVDF) homopolymer, respectively, as the polymeric component. The additive was diallyl 4,4'-sulfonyl dibenzoate. The room temperature and elevated temperature properties of the compression molded and crosslinked samples are set forth in Table IV. The elevated temperature and hot modulus results were at 250° C for E/CTFE and at 200° C for PVDF.

                                      TABLE IV                                     __________________________________________________________________________                         Room Temperature                                                                           Elevated Temperature                           __________________________________________________________________________                   Radiation                                                                            Tensile                                                                             Elongation                                                                            Tensile                                                                             Elongation                                              Dose  Strength                                                                            (10"/min.)                                                                            Strength                                                                            (10"/min.)                                                                            Hot Modulus                        Composition   (MR)  (psi)                                                                               (%)    (psi)                                                                               (%)    50 psi                             __________________________________________________________________________     E/CTFE alone  10    6426 263     18  680    Would not sup-                                   20    5127 213     37  124    port 50 psi                        E/CTFE   100 g.                                                                              10    6396 175    106  136    37                                 Diallyl Ester                                                                            5 g.                                                                 MgO       1 g.                                                                               20    6045 146    125  106    27                                 PVDF alone    10    3776 220     70  435    302                                              20    3979 117     66  104    67                                 PVDF     100 g.                                                                              10    5841 329    174  147    33                                 Diallyl Ester                                                                            5 g.                                                                               20    4135 158    146   97    24                                 __________________________________________________________________________

EXAMPLE 6

The samples of Example 5 were aged at elevated temperatures after irradiation crosslinking and tested for tensile strength (psi) and elongation (%) after cooling to room temperature. The E/CTFE copolymer was aged at 225° C and the PVDF homopolymer at 200° C. The results are set forth in Table V.

                                      TABLE V                                      __________________________________________________________________________                Radi-                                                                              Aging Period (Days)                                             __________________________________________________________________________                ation                                                                          Dose                                                                               0       1       3       5       7       11                      __________________________________________________________________________     Composition                                                                               (MR)                                                                               T.S.                                                                               Elong.                                                                             T.S.                                                                               Elong.                                                                             T.S.                                                                               Elong.                                                                             T.S.                                                                               Elong.                                                                             T.S.                                                                               Elong.                                                                             T.S.                                                                               Elong.              __________________________________________________________________________     E/CTFE alone                                                                              10  6426                                                                               263 5972                                                                               229 5003                                                                               194 4632                                                                               171 4620                                                                               113 4143                                                                               58                             20  5127                                                                               213 5382                                                                               192 4958                                                                               167 4882                                                                               121 4560                                                                                96 4602                                                                               54                  E/CTFE 100g                                                                               10  6396                                                                               175 5846                                                                               158 5107                                                                               117 5067                                                                               127 5048                                                                               117 4729                                                                                100                Diallyl Ester                                                                          5g                                                                     MgO     1g 20  6045                                                                               146 5118                                                                                96 4736                                                                                88 5141                                                                                88 3429                                                                               183 4786                                                                                500                PVDF alone 10  3776                                                                               220 4108                                                                               417 3782                                                                               267 3663                                                                               269 3548                                                                               158 4024                                                                                329                           20  3779                                                                               117 3270                                                                               113 3466                                                                               118 3436                                                                                75 4745                                                                                58 3528                                                                               58                  PVDF   100g                                                                               10  5841                                                                               329 4098                                                                               300 4941                                                                               267 4464                                                                               267 3955                                                                               146 4528                                                                                275                Diallyl Ester                                                                           5g                                                                               20  4135                                                                               158 4225                                                                               192 3737                                                                                71 3896                                                                                71 3755                                                                                96 4004                                                                               46                  __________________________________________________________________________

Three additional samples were prepared by powder blending as set forth in Example 3. The three compositions were:

    ______________________________________                                         1 -   E/TFE copolymer alone.                                                   2 -   E/TFE copolymer         100     gms.                                           MgO                     0.5     gms.                                           Diallyl 4,4'-sulfonyl dibenzoate                                                                       5       gms.                                           Irganox 1010* (antioxidant)                                                                            0.25    gms.                                           *Irganox 1010 is tetrakis (methylene                                           3-(3', 5'-di-tert-butyl-4'-hydroxy-                                            phenyl) propionate) methane                                              3 -   E/TFE copolymer         100     gms.                                           MgO                     0.5     gms.                                           Diallyl 4,4'-sulfonyl dibenzoate                                                                       3       gms.                                           Triallyl trimesate      2       gms.                                           Irganox 1010            0.25    gms.                                     ______________________________________                                    

The three samples in powdered form were extruded through an extruder head having a head temperature of 277° C to form rods. The rods were then pelletized and the pellets were extruded onto the surface of an 18 AWG bare copper wire to form a 10 to 15 mil coating. The extrusion conditions were as follows:

    ______________________________________                                                Temperature (° C)                                                       Barrel Zones                                                            ______________________________________                                         Composition                                                                             1        2        3      Die    Head                                  ______________________________________                                         1        304      316      316    354    377                                   2        266      282      293    329    357                                   3        271      282      293    329    357                                   ______________________________________                                    

The insulated wires were then subjected to irradiation with high energy electrons by a 1.0 mev. resonant beam transformer. The resulting insulated wires with irradiation crosslinked coatings were then annealed and subsequently tested to determine their mechanical and electrical properties. The results of these tests on the wire samples are set forth in Table VI.

                                      TABLE VI                                     __________________________________________________________________________                  COMPOSITION OF WIRE COATING                                       __________________________________________________________________________                  1       2          3                                                                              (With diallyl and                                           (No additive)                                                                          (With diallyl ester)                                                                      triallyl ester)                                __________________________________________________________________________     Test         10MR                                                                               20MR                                                                               10MR  20MR 10MR 20MR                                      __________________________________________________________________________     Room Temperature                                                               Tensile Strength (psi)                                                                      5229                                                                               5480                                                                               6603  6832 5651 5864                                      Elongation (%)                                                                               133                                                                               170 225   225  119   108                                      At 250° C                                                               Tensile Strength (psi)                                                                       340                                                                               290 471   567  321   351                                      Elongation (%)                                                                               700                                                                               395 338   455  133   78                                       Hot Modulus  Failed                                                                             280  83    65   86   29                                       (275° C/50 psi)                                                         High Voltage Cut-thru                                                                       Failed                                                                             Failed                                                                             Passes at 200° C,                                                                  Passes at 250° C,                       (at 250° C one lb.                                                                           1 1/2 lb. load                                                                            1 lb. load on                                  load on each end     on each end (10                                                                           each end (15 mils                              and 900 V(rms))      mils insulation                                                                           insulation                                                          thickness) thickness)                                     __________________________________________________________________________      Table VI indicates that both room temperature and elevated temperature      properties of irradiation cured wire coatings, containing the diallyl      esters of the invention, were in most cases better, and in some cases      considerably better, than the equivalent coatings without the esters. High      voltage cut-through properties were especially outstanding, particularly      in the case of composition 3 containing the diallyl ester in combination      with a trifunctional crosslinking agent. 

I claim:
 1. Wire coated with an irradiation cured polymeric composition comprising a high temperature processing fluorocarbon polymer selected from the group consisting of polymers and copolymers of ethylene-tetrafluoroethylene, ethylene-chlorotrifuloroethylene, vinylidene fluoride, tetrafluoroethylene-vinylidene fluoride, tetrafluoroethylene-hexafluoropropylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene and blends thereof and as a crosslinking agent a compound of the formula: ##SPC3##in which R₁ and R₂ are independently selected from the group consisting of allyl and methallyl, the crosslinking agent being present in an amount of from 0.5 to 20 parts by weight per hundred parts of the fluorocarbon polymer sufficient to plasticize the polymer and to impart deformation resistance upon cross-linking. 